The invention concerns a device for the optical scanning of objects, especially markings, with an apparatus that has first and second transmitters emitting respective first and second light beams, a rotatable polygonal mirror which directs the light beams onto the marking and which deflects light reflected by the markings, and a receiver system for receiving the reflected light.
A device of this kind, a so-called scanner, is known from EP 0 480 348 A1. In that device, the light beams from two transmitters, especially lasers, are deflected by a semitransparent mirror into a common beam direction and strike a rotating polygonal mirror which directs the light beams onto the markings being scanned, such as a barcode. The light returned by the markings is deflected by the polygonal mirror to a common receiver system. The two transmitters have different focal distances so as to be able to scan and read markings at different distances from the device. The two transmitters are at first alternatingly operated, in order to establish which focal distance corresponds to the distance from the markings being scanned. After this, only the transmitter which has the appropriate distance is used to scan and read the marking. The two transmitters with different focal distance give the device an improved field depth.
U.S. Pat. No. 6,527,184 B1 discloses a device with two pairs of transmitters of the kind familiar from EP 0 480 348 A1. The light beams of the respective two pairs of transmitters, coinciding in a common axis, are in different planes which are offset from each other in the direction of the axis of rotation of the polygonal mirror. This is supposed to equalize the parallax which can occur in the case of different distances.
EP 0 643 362 A1 discloses a device in which the light beam of a transmitter is deflected by a rotating polygonal mirror and an angular mirror onto the marking being scanned. The two mirror planes of the angular mirror that are oriented at an angle to each other deflect the scanning plane of the light beam into two intersecting scanning planes, through which the light beam passes in succession. There is only one receiving system, which evaluates the information from the successively traveled scanning plane. Scanning in two intersecting planes enables an omnidirectional reading of a barcode or line code.